Poly(vinyl alcohol) fluidized polymer suspensions

ABSTRACT

At least 20% of poly(vinyl alcohol) (PVA) is dispersed in an aqueous solution of at least one salt dissolved therein selected from the group of sodium or potassium formate, sodium, potassium, or magnesium sulfate, sodium or potassium citrate, sodium or potassium polyacrylate, or mixtures thereof. This aqueous suspension of PVA is useful in systems in which PVA is dissolved in order to reduce the time of dissolution.

This invention relates to fluid suspensions of poly(vinyl alcohol) inaqueous systems that contain specific dissolved salts.

BACKGROUND OF THE INVENTION

Prior to the present invention, poly(vinyl alcohol) (hereinafterreferred as "PVA") has traditionally been handled in its dry,particulate form. The water soluble forms of PVA are known to be 77 to99.8% hydrolyzed. Problems associated with dry PVA include undesirabledust generation, poor dispersibility when added to aqueous systems, andundesirably long dissolution times.

The dust associated with dry, particulate PVA presents the sameconventional handling problems as are encountered with other particulatematerials.

When added to aqueous systems, PVA tends to agglomerate to form clumps.Agglomeration can be reduced in many cases by adding the polymer to theaqueous system slowly with agitation. Slow dissolution substantiallyreduces the speed of manufacturing operations.

For the above reasons, plant operators desire a fast, effective, andsimple way of incorporating PVA into an aqueous system. In other words,users of PVA desire a stable, concentrated, PVA suspension that can beused to incorporate PVA into aqueous solutions readily, withoutformation of agglomerates or clumps, and which may be handled withoutthe problems associated with a dry powder.

Several formulations exist in the prior art that describe suspensionsystems of various water soluble polymers that avoid the above mentionedproblems. For example, U.S. Pat. No. 4,883,536 discloses an aqueoussuspension of at least 15% by total weight of the suspension, of atleast one anionic or nonionic water-soluble polymer dispersed in anaqueous solution of an ammonium salt having a multivalent anion, whereinthe weight ratio of the ammonium salt to the water is at least 0.15.Another example is U.S. Pat. No. 4,883,537 that discloses the use ofpotassium carbonate in aqueous suspensions of sodiumcarboxymethylcellulose.

The present invention overcomes the above mentioned problems inindustrial practice in a different manner than the above prior art byusing different types of salts for preparing fluidized suspensions ofPVA.

SUMMARY OF THE INVENTION

The present invention is directed to an aqueous suspension comprising atleast 20% by total weight of the suspension, of poly(vinyl alcohol)dispersed in an aqueous solution of at least one salt selected from thegroup consisting of sodium or potassium formate, sodium, potassium, ormagnesium sulfate, sodium or potassium citrate, sodium or potassiumpolyacrylate and mixtures thereof.

This invention also relates to a method of using the aqueous suspendedproduct of this invention in paper size press applications.

DETAILED DESCRIPTION OF THE INVENTION

It has been found that aqueous fluid suspensions of 20% by weight orgreater of poly(vinyl alcohol) can be prepared by dispersing the PVA inwater that contains appropriate concentrations of selected salts withoutcausing the PVA to thicken to a paste consistency. These fluidizedpolymer suspensions of PVA can be used in many applications. Such PVAsuspensions dissolve significantly faster, when added to dilution water,as compared to dry PVA.

The water solubility of PVA varies as a function of the polymer's degreeof hydrolysis. The water soluble varieties of PVA range in degree ofhydrolysis from 77 to 99.8%. PVA with a degree of hydrolysis from 87 to90% has the highest solubility in cold water (i.e., ambient or less).

A number of salts are useful to prepare aqueous suspensions of PVA.These included sodium or potassium formate, sodium, potassium ormagnesium sulfate, sodium or potassium citrate, and sodium or potassiumpolyacrylate. Sodium formate and sodium sulfate are preferred salts.Mixtures of salts such as sodium formate with sodiumcarboxymethylcellulose or styrene maleic anhydride copolymer can also beemployed to prepare suspensions of the PVA.

The salts of this invention should be present in the suspension in theamount of from about 10% to about 40% (preferably, 10% to about 20%) byweight, based on the total weight of the suspension. The ratio of saltto water in the suspension is 1:1 to 1:7.

Although water is the normal carrier medium for this invention, theincorporation of glycerin into the fluid suspension was effective toimprove film properties of the suspension (as compared to dry PVA) inthe cases where the suspension, or dry PVA, was dissolved in water thencast as a film. Other additives such as sodium alginate or hydrophobicsizing agents (e.g., rosin soap, dispersed rosin size, wax emulsions,polyethylene emulsions, alkyl ketene dimer, and alkyl succinicanhydride) may also be incorporated into fluidized polymer suspension ofthis invention.

Suspensions, according to this invention, contain from about 15% toabout 35% of PVA, preferably 20% to 25%, by weight, based on the totalweight of the suspension.

A number of other additives can be present in the present invention toprovide beneficial properties to the suspension. Stabilizers are apreferred additive such as xanthan gum or sodium carboxymethylcellulose.These stabilizers increase the time over which the suspension willremain stable. Stabilizers in the instant invention are typicallypresent in the amount of up to 1.5%, and are preferably used in anamount of 0.05% to 0.25%.

Other additives that can be used include preservatives, such as ProxelGXL (marketed by ICI), in an amount of up to 0.3%, preferably about0.1%. Dispersants, surfactants, glycols, pigments, and thickening agentscan also be incorporated into the PVA suspension of this invention whenneeded for a particular application. These can be generally used inamounts up to 10% by weight of the total suspension.

In a preferred embodiment of the invention, a suspension of 20-25% byweight of PVA was prepared by adding this water soluble polymer to anaqueous solution of concentrated sodium formate to form a fluid pourablesuspension. This suspension can give useful performance properties in apaper size press, calendar stack, or paper coating applications.

In a second preferred embodiment of the present invention, a fluidpourable suspension of 20-25% by weight of PVA was prepared in a mediumincluding a dissolved salt such as sodium sulfate or potassium sulfate,glycerin and water.

The PVA suspensions of this invention can be prepared by dissolving thesalt in water to form an aqueous salt solution and, then, dispersingwith agitation the PVA therein. In the case where other additives areemployed, these are typically added to the water before the salt. Insome instances, heat may be needed to effect readily the dissolution ofcertain salts.

The PVA suspensions of this invention are useful in virtually allapplications where dry PVA polymers are presently being used. Theapplications in which the dispersions of this invention may be usedinclude textiles, adhesives, paper, construction materials, and otherapplications where dry PVA is currently being used.

The advantages of the present invention as compared to the prior art useof dry powdered PVA include: 1) the elimination of dust in handling ofthe PVA; 2) a faster dissolution rate and the elimination of lumping ofthe PVA when added to dilution water; 3) significantly reduced foamingof the PVA in solution; 4) improved performance in a paper size pressapplication; and 5) in the case of PVA suspensions in salt, glycerine,and water, more flexible film properties of the invention in end useapplication.

The suspensions of this invention have a long shelf life withoutseparating and can readily be added to aqueous systems by simply adding,e.g., pouring, the suspension into the aqueous system. Agitationenhances dissolution. The manner in which this suspension is used in theindustry is limited only by the limitation placed on aqueoussuspensions.

This invention will be further illustrated by the following examples.

EXAMPLE 1

A quantity of 57.2 parts by weight of water was added to a mixing vesseland 0.20 parts by weight of xanthan gum was added to the water andstirred to dissolve. After the xanthan gum dissolved, 17.5 parts byweight of sodium formate was added to the water and stirred to dissolve.Following the sodium formate dissolution step, 25 parts by weight ofAirvol® 540S, high viscosity poly(vinyl alcohol) (available from AirProducts Company) were added to the water and stirred to disperse. In afinal step, 0.1 parts of Proxel® GXL preservative was added to thesuspension.

It was observed that the final product was very fluid and pourable. ThePVA particles did not dissolve in the concentrated sodium formateaqueous solution but instead appeared to swell in this medium. Theviscosity of this suspension was measured with a Stormer viscometer (awidely use instrument in the latex paint industry for measuringviscosity) and found to be 100 Krebs Units ("KU") in viscosity.Generally, suspensions with a viscosity of greater than 135 KU would notbe considered useful because their high viscosity would preclude ease ofhandling.

In a comparative experiment, the same procedure was employed as aboveexcept that 25 parts by weight of Natrosol® 250LR polymer (marketed byAqualon Company) was added to the aqueous sodium formate solutioninstead of the PVA. In this case, a fluid suspension of the watersoluble polymer was not observed, but instead a thick unusable paste wasobtained.

Natrosol 250LR hydroxyethylcelluose (HEC) is a nonionic water solublepolymer similar in hydroxyl functionality and molecular weight comparedto Airvol® 540S polymer. Despite these similarities, it was shown inthis example that the Natrosol 250LR HEC did not yield a fluidsuspension in the same medium that was suitable for PVA. This examplethus shows that PVA behaves much differently in aqueous media thatcontain dissolved salts as compared to Natrosol® 250LRhydroxyethylcellulose polymer.

EXAMPLE 2

A quantity of 0.2 parts by weight of xanthan gum was added to 69.7 partsby weight of water and stirred to dissolve. After the xanthan gumdissolved, 10 parts by weight of sodium sulfate was added to the waterand stirred to dissolve. Heating was found to be useful to make thesodium sulfate dissolution step proceed. After the sodium sulfatedissolved, 20 parts by weight of Airvol® 540 polymer was added to thesolution and stirred to disperse. As a final step, 0.1 parts of Proxel®GXL material was added to the suspension as a preservative. A fluidpourable suspension was obtained. This suspension was found to have aStormer viscosity of 86 Kreb Units ("KU").

As a control experiment, Natrosol® 250LR hydroxyethylcellulose wassubstituted for Airvol® 540 PVA in the above suspension formulation. Inthis case, a fluid suspension was obtained initially but then gelled toa thick paste after 1 hour.

As another control experiment, Airvol® 540S polymer was substituted forAirvol® 540 in the above suspension formulation. The polymer Airvol®540S has a finer particle distribution than Airvol® 540. In this secondcomparative experiment, a thick paste was obtained with a Stormerviscosity of greater than 140 Kreb Units.

EXAMPLE 3

The same procedure as in Example 2 above was used to prepare asuspension of Airvol® 540 PVA except, in this instance, potassiumsulfate was substituted for sodium sulfate. A fluid pourable suspensionwas observed with a Stormer viscosity of 103 Kreb Units.

EXAMPLE 4

The same procedure as in Example 3 was used with the exception thatAirvol® 803 PVA (a low molecular weight PVA) was substituted for Airvol®540 as the PVA ingredient. In this experiment, a fluid suspension of thePVA was obtained with a Stormer viscosity of 82 Kreb Units.

This example showed that PVA of various molecular weights could be usedin the present invention.

EXAMPLE 5

To 95 parts by weight of the fluidized polymer suspension from Example1, 5 parts by weight of 50% rosin soap sizing agent was added. Theresultant mixture was observed to be a fluid suspension with a Stormerviscosity of 95 Kreb Units.

EXAMPLE 6

A quantity of 1 part by weight of Kelgin XL sodium alginate (marketed byKelco Inc.) was added to 54 parts by weight of water and was stirred todissolve. After dissolution occurred, 20 parts by weight of sodiumformate were added to the water and stirred to dissolve. As a finalstep, 25 parts by weight of Airvol® 540S were added to the mixture andstirred. A fluid suspension with a Stormer viscosity of 61 Kreb Unitswas obtained.

COMPARATIVE EXAMPLE A

Suspensions were attempted of 20% by weight Airvol® 540S PVA inconcentrated aqueous solutions using the following salts: sodiumchloride, sodium acetate, Ambergum 3021 sodium carboxymethylcellulose,Scripset 700 (Hercules) styrene maleic anhydride copolymer, aluminumsulfate (18 hydrate), and potassium bicarbonate. However, in each ofthese cases a fluid suspension was not obtained. A summary of thespecific formulations attempted is shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        UNSUCCESSFUL ATTEMPTS TO                                                      PREPARE FLUID 20 WT % PVA SUSPENSIONS                                                                                 Stormer                                    Water   Xanthan  Salt        PVA   Viscosity                             Test (parts) (parts)  (parts)     (parts)                                                                             (KU)                                  ______________________________________                                        a    46.8    0.2      NaCl      33  20    >140                                b    46.8    0.2      sodium acetate                                                                          33  20    >140                                c    59.8    0.2      potassium 20  20    >140                                                      bicarbonate                                             d    --      --       Ambergum  80  20    >140                                                      3021                                                    e    --      --       Scripset 700                                                                            80  20    >140                                f    64.8    0.2      Aluminum  15  20    >140                                                      sulfate.18 H.sub.2 O                                    ______________________________________                                    

This comparative example demonstrated that not all aqueous saltsolutions are suitable for the preparation of fluid suspensions withinthe scope of this invention of 20% or greater PVA content.

EXAMPLE 7

Fluid suspensions were prepared of Airvol® 540S in aqueous systemscontaining using the following salts: magnesium sulfate, potassiumcarbonate, sodium citrate, potassium citrate, and Dispex N-40 (AlliedColloids--40% sodium polyacrylate in water). In each of these cases,fluid pourable suspensions of 20 wt % PVA were observed. The specificformulations are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________    SUCCESSFUL 20% SUSPENSIONS                                                    OF PVA IN AQUEOUS SALT SOLUTIONS                                                                                 Stormer                                       Water     Salt        PVA       Viscosity                                  Test                                                                             (parts)                                                                           (parts)                                                                             (parts)     (parts)   (KU)                                       __________________________________________________________________________           CMC-7L1T                                                               a  58  2.0   Na citrate                                                                              20                                                                              Airvol ™ 540S                                                                      20                                                                              82                                         b  58  2.0   Potassium citrate                                                                       20                                                                              Airvol ™ 540S                                                                      20                                                                              76                                         c  --  --    Dispex N-40                                                                             80                                                                              Airvol ™ 540S                                                                      20                                                                              122                                               xanthan                                                                d  59.85                                                                             0.15  potassium carbonate                                                                     20                                                                              Airvol ™ 540S                                                                      20                                                                              65                                         e  64.85                                                                             0.15  magnesium sulfate                                                                       15                                                                              Airvol ™ 540S                                                                      20                                                                              82                                         __________________________________________________________________________

EXAMPLE 8

Fluid suspensions were prepared of PVA in mixtures of salts in which oneof the salt components was polymeric in nature.

In one of these experiments, 100 parts by weight of the fluid suspensionfrom Example 1 were mixed with 85 parts by weight of Ambergum 3021sodium carboxymethylcellulose and parts by weight of Airvol® 540Spolymer, such that the final PVA content was 20% by weight. The finalproduct was a fluid pourable suspension having a Stormer viscosity of115 Kreb Units.

In a like experiment, 100 parts by weight of the suspension from Example1 were mixed with 85 parts by weight of Scripset 700 styrene maleicanhydride copolymer and 15 parts by weight of Airvol® 540S polymer. Thisformulation yielded a fluid pourable suspension containing 20% by weightof PVA having a Stormer viscosity of 116 Kreb Units.

EXAMPLE 9

A sample of 40 grams of the polymer suspension of Airvol® 540S polymerof Example 1 was added to 160 grams of dilution water while stirring. Itwas observed that the suspension dispersed readily without lumps. Theviscosity of the water to which the fluid PVA suspension had been addedwas observed to increase rapidly. There was very little foam evident.After 15 minutes of stirring, the PVA appeared to be predominantlydissolved. This solution was poured through a 100 mesh screen and foundto show relatively few insoluble gel particles. The +100 mesh materialwas washed into a tared container and dried and the final weight ofinsoluble gel particles was found to be approximately 0.01 grams.

For comparative purposes a quantity of 10 grams of dry powdered Airvol®540S PVA was added to 190 grams of water with good agitation. The dryPVA was added slowly and uniformly to the water to try to obtain gooddispersion of the polymer in the water; however, in spite of the abovementioned precautions taken, lumping of the PVA was observed as it wasadded to the water. When the PVA and water mixture was stirred todissolve the PVA, significant foam generation was also observed. After15 minutes of stirring, the PVA solution was filtered through a 100 meshscreen. A number of undissolved lumps and gel particles were observed.The dried weight of these +100 mesh gel particles was 0.2 grams.

This experiment demonstrated that a fluid suspension of PVA of thepresent invention gave significant improvements in solution preparationas compared to dry powdered PVA. These improvements were threefold indimension: 1) the elimination of PVA lump formation upon addition todilution water; 2) more rapid dissolution of the PVA; and 3) asignificant reduction in the quantity of foam generated in the PVAsolution.

EXAMPLE 10

In a paper size press application, 40 lbs/ream basis weight paper with astarting Gurley porosity value of 30 seconds was treated with an 8%solution of Stayco C starch at 65° C. The wet weight pickup of thestarch solution onto the paper in these tests was 30% of basis weight.In separate size press tests, the starch solution used to surface-treatthe paper was modified with various levels of either dry Airvol® 540Spolymer as an additive, or with various levels of the fluid suspensionof Airvol® 540S suspension product from Example 1. These additives wereextensively cooked with the starch in separate preparations to assureadequate dissolution.

The results from these size press tests are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        GURLEY POROSITY VALUES                                                        OF SIZE PRESS TREATED PAPER                                                                           Gurley Porosity                                                               of Treated Paper                                      Tpye of Size Press Treatment Treated Paper                                                            (seconds)                                             ______________________________________                                        None                    30                                                    8% Starch Only, No Modifier                                                                           46                                                    8% Starch with 0.25% Dry Airvol ™ 540S                                                             81                                                    8% Starch with 0.30% Dry Airvol ™ 540S                                                             89                                                    8% Starch with 0.5% Dry Airvol ™ 540S                                                              154                                                   8% Starch with 0.25% Airvol ™ 540S                                                                 80                                                    (Active), PVA Fluid Suspension                                                8% Starch with 0.3% Airvol ™ 540S                                                                  122                                                   (Active) PVA Fluid Suspension                                                 8% Starch with 0.5% Airvol ™ 540S                                                                  212                                                   (Active), PVA Fluid Suspension                                                ______________________________________                                    

These tests show that at higher concentrations the fluidized polymersuspension of PVA from Example 1 unexpectedly gave significantlyimproved size press treatment results of the paper as compared to dryPVA at equal active dosage.

EXAMPLE 11

The polymer suspensions of PVA from Examples 1, 2, 3, 4, 5, 6, 7, and 8were added to dilution water and stirred to dissolve at a final solutionconcentration of 5% active PVA. These solutions were then allowed tostand in jars for a period of 16 hours or longer.

It was observed in the case of the sodium formate polymer suspension ofExample 1, that only a relatively minor quantity of settled insolublematerial was observed in the PVA solution. This insoluble materialconstituted a settled layer of approximately 5% of the volume of thestorage container. This material was readily dispersible in water.

It was observed in the case of the fluid polymer suspension of PVAprepared in Dispex N-40 from Example 6 that an extremely viscous settledlayer, comprising approximately 10% of the volume of the storagecontainer, was observed. The top most phase of the stored solution inthis case was clear and very fluid. This two phase separation couldpotentially have utility in some as yet undefined application.

It was found in the case where sodium formate was employed inconjunction with salts, such as sodium carboxymethylcellulose or styrenemaleic anhydride copolymer (SMA) from Example 4, that significant phaseseparation of the PVA solution was observed. In the case of the polymersuspension containing SMA, a clear bottom layer was observed.

In all of the other PVA solutions, a significant quantity of undissolvedmaterial, constituting greater than 10% of the volume of the storagecontainers, was observed. The salts present in these systems includedsodium sulfate, potassium sulfate, magnesium sulfate, sodium citrate,potassium citrate, and potassium carbonate.

It was shown in this Example that sodium formate was a preferred saltfor preparing fluid suspensions of PVA that would have as their intendeduse a concentrated solution of PVA in dilution water.

EXAMPLE 12

The fluid suspensions of PVA from Examples 1, 2, 3, 4, 5, 6, 7, and 8were added to dilution water in a ratio so as to yield 1% active PVAsolutions after stirring to dissolve. These solutions were allowed tostand for 16 hours and then checked for the presence of insolublematerial.

It was found in all cases that only a very small quantity of undissolvedPVA was observed in these tests. It was thus demonstrated that the PVAsuspensions of Examples 1, 2, 3, 4, 5, 6, 7, and 8 are useful forpreparing dilute solutions of PVA.

EXAMPLE 13

Fifty gram quantities of the 1% active aqueous solutions of PVA preparedin Example 12 were added to aluminum pans and dried in an oven at 50° C.For comparative purposes, a control film was also prepared by drying a1% active solution of Airvol® 540S in an aluminum pan.

In the control case, a clear continuous film was obtained after dryingthe PVA solution.

In the case of the PVA sample prepared in aqueous potassium carbonate(Example 7), the dried 1% active PVA solution did not form a continuousfilm but was instead a weak crusted mixture of salt and polymer. Thisresult showed that potassium carbonate would not be useful to preparefluidized polymer suspensions of PVA with end use utility as a filmformer.

In the case where fluid polymer suspensions of PVA were prepared insodium sulfate, potassium sulfate or magnesium sulfate, from Examples 2,3, 4, and 7, the dried films of the 1% active PVA solutions preparedfrom these samples were fairly clear, with little or no crystallizedsalt evident in the dried films. Sulfate salts, therefore, appear tointegrate into the PVA film as this is formed during drying of the PVAsolutions.

In the case of all the other films derived from PVA solutions that hadbeen prepared from various polymer suspension systems, significant saltseparation from the PVA films and crystallization occurred. Hazy filmswere observed in all of these cases. This applied for sodium formate,sodium citrate, potassium citrate, and Dispex® N-40, as well as mixturesof these salts.

This Example showed that sulfate salts were preferred for preparingfluid suspensions of PVA in the cases where clarity of the final PVAfilm would be a critical parameter of the PVA end use performance.

EXAMPLE 14

To 90 parts by weight of the suspension from Example 2 eight parts byweight of glycerin were added with stirring; then 2 parts by weight ofAirvol® 540S were added to suspension and glycerin mixture, such thatthe final mixture was maintained at 20% by weight PVA. A fluid pourablesuspension was observed.

The above suspension was added to dilution water at a ratio to yield a1% active PVA solution and stirred to dissolve the PVA. This solutionwas then added to an aluminum pan and dried at 50° C.

The resultant film was found to be essentially clear and continuous.This film was found to be far less brittle than the control film ofstraight PVA in water from Example 13. The improved flexibility of thefilm obtained from a mixed polymer suspension system containing glycerincould be of value for a number of film applications in which PVA couldbe employed.

This Example demonstrated the utility of employing additional componentssuch as glycerin in a formulated aqueous PVA polymer suspension toimpart desirable final properties to PVA.

What is claimed:
 1. An aqueous suspension comprising at least 20% bytotal weight of the suspension, of poly(vinyl alcohol) dispersed in anaqueous solution of at least one salt dissolved therein selected fromthe group consisting of sodium or potassium formate, sodium or potassiumcitrate, sodium or potassium polyacrylate and mixtures thereof, and asuspension stabilizer.
 2. The suspension of claim 1 wherein thepoly(vinyl alcohol) is 87-90% hydrolyzed.
 3. The suspension of claim 1wherein the dissolved sodium formate is further admixed with sodiumcarboxymethylcellulose or styrene maleic anhydride.
 4. The suspension ofclaim 1 wherein the suspension contains xanthan gum as a suspensionstabilizer.
 5. The suspension of claim 1 wherein the suspension containsglycerin.
 6. The suspension of claim 1 wherein the suspension containssodium alginate.
 7. The suspension of claim 1 wherein the suspensioncontains hydrophobic sizing agents.